Bicycle damping enhancement system

ABSTRACT

A bicycle shock absorber and methods for differentiating between rider-induced forces and terrain-induced forces includes a first fluid chamber having fluid contained therein, a piston for compressing the fluid within the fluid chamber, a second fluid chamber coupled to the first fluid chamber by a fluid communication hose, and an inertial valve disposed within the second fluid chamber. The inertial valve opens in response to terrain-induced forces and provides communication of fluid compressed by the piston from the first fluid chamber to the second fluid chamber. The inertial valve does not open in response to rider-induced forces.

RELATED APPLICATIONS

Related applications are identified in an application data sheet (ADS)filed with this application.

INCORPORATION BY REFERENCE

The entireties of all applications listed in the ADS filed herewith arehereby expressly incorporated by reference herein and made a part of thepresent disclosure.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to the field of bicycle suspensions.More particularly, the invention relates to a damping enhancement systemfor a bicycle.

2. Description of the Related Art

For many years bicycles were constructed using exclusively rigid framedesigns. These conventional bicycles relied on air-pressurized tires anda small amount of natural flexibility in the frame and front forks toabsorb the bumps of the road and trail. This level of shock absorptionwas generally considered acceptable for bicycles which were riddenprimarily on flat, well maintained roads. However, as “off-road” bikingbecame more popular with the advent of All Terrain Bicycles (“ATBs”),improved shock absorption systems were needed to improve the smoothnessof the ride over harsh terrain. As a result, new shock absorbing bicyclesuspensions were developed.

Two such suspension systems are illustrated in FIGS. 1 and 2. These tworear suspension designs are described in detail in Leitner, U.S. Pat.No. 5,678,837, and Leitner, U.S. Pat. No. 5,509,679, which are assignedto the assignee of the present application. Briefly, FIG. 1 illustratesa telescoping shock absorber 110 rigidly attached to the upper armmembers 103 of the bicycle on one end and pivotally attached to thebicycle seat tube 120 at the other end (point 106). FIG. 2 employsanother embodiment wherein a lever 205 is pivotally attached to theupper arm members 203 and the shock absorber 210 is pivotally attachedto the lever 205 at an intermediate position 204 between the ends of thelever 205.

There are several problems associated with the conventional shockabsorbers employed in the foregoing rear suspension systems. One problemis that conventional shock absorbers are configured with a fixed dampingrate. As such, the shock absorber can either be set “soft” for betterwheel compliance to the terrain or “stiff” to minimize movement duringaggressive pedaling of the rider. However, there is no mechanism in theprior art which provides for automatic adjustment of the shock absorbersetting based on different terrain and/or pedaling conditions.

A second, related problem with the prior art is that conventional shockabsorbers are only capable of reacting to the relative movement betweenthe bicycle chassis and the wheel. In other words, the shock absorberitself has no way of differentiating between forces caused by the upwardmovement of the wheel (i.e., due to contact with the terrain) and forcescaused by the downward movement of the chassis (i.e., due to movement ofthe rider's mass).

Thus, most shock absorbers are configured somewhere in between the“soft” and “stiff” settings (i.e., at an intermediate setting). Using astatic, intermediate setting in this manner means that the “ideal”damper setting—i.e., the perfect level of stiffness for a given set ofconditions—will never be fully realized. For example, a rider, whenpedaling hard for maximum power and efficiency, prefers a rigidsuspension whereby human energy output is vectored directly to therotation of the rear wheel. By contrast, a rider prefers a softersuspension when riding over harsh terrain. A softer suspension settingimproves the compliance of the wheel to the terrain which, in turn,improves the control by the rider.

Accordingly, what is needed is a damping system which will dynamicallyadjust to changes in terrain and/or pedaling conditions. What is alsoneeded is a damping system which will provide to a “stiff” damping rateto control rider-induced suspension movement and a “soft” damping rateto absorb forces from the terrain. Finally, what is needed is a dampingsystem which will differentiate between upward forces produced by thecontact of the wheel with the terrain and downward forces produced bythe movement of the rider's mass.

SUMMARY OF THE INVENTION

An embodiment involves a bicycle having a bicycle frame and a pedalcrank assembly supported by the bicycle frame and configured to bedriven by rider-induced pedaling forces. The bicycle also includes awheel and a suspension assembly interposed between the bicycle frame andthe wheel. The suspension assembly includes a spring that applies aforce tending to extend the suspension assembly. A damper includes adamper tube and a piston rod supporting a piston in sliding engagementwith the damper tube. The piston and the damper tube at least partiallydefine a compression chamber that decreases in volume during compressionmovement of the suspension assembly. The damper additionally includes aninertia valve having an inertia mass that is normally biased to a closedposition in which the inertia mass is adjacent an opening to thecompression chamber such that fluid flow through the opening isinhibited. The inertia mass is movable to an open position in which theinertia mass is not adjacent the opening such that fluid flow throughthe opening is not inhibited. The inertia valve remains in the closedposition in response to the rider-induced pedaling forces applied to theframe and the inertia valve moves toward the open position in responseto a terrain-induced force above a predetermined threshold applied tothe wheel. A sensitivity adjuster has a first adjustment position and asecond adjustment position. The inertia valve has a first sensitivity inthe first adjustment position and the inertia valve has a secondsensitivity in the second adjustment position, wherein the secondsensitivity is different from the first sensitivity.

An embodiment involves a method of providing for adjustment of a bicycleshock absorber, including providing a bicycle shock absorber comprisinga spring that applies a force tending to extend the suspension assembly,a damper tube, a piston supported on a piston rod and in slidingengagement with the damper tube. The piston and the damper tube at leastpartially define a compression chamber that decreases in volume duringcompression movement of the suspension assembly. The damper alsoincludes an inertia valve including an inertia mass that is normallybiased to a closed position wherein the inertia mass is adjacent anopening to the compression chamber such that fluid flow through theopening is inhibited and is movable to an open position wherein theinertia mass is not adjacent the opening such that fluid flow throughthe opening is not inhibited. The inertia valve remains in the closedposition in response to the rider-induced pedaling forces applied to theframe and the inertia valve moves toward the open position in responseto a terrain-induced force above a predetermined threshold applied tothe wheel. A sensitivity adjuster is provided for the inertia valve. Afirst adjustment position of the sensitivity adjuster is provided inwhich the inertia valve has a first sensitivity to terrain-inducedforces. A second adjustment position of the sensitivity adjuster isprovided in which the inertia valve has a second sensitivity toterrain-induced forces that is different from the first sensitivity. Thesensitivity adjuster is allowed to be set to either of the firstadjustment position or the second adjustment position.

An embodiment involves a method of operating a bicycle shock absorber,which includes operating a bicycle shock absorber with a sensitivityadjuster positioned in a first adjustment position. The bicycle shockabsorber includes a spring that applies a force tending to extend thesuspension assembly. The shock absorber also includes a damper tube anda piston supported on a piston rod and in sliding engagement with thedamper tube. The piston and the damper tube at least partially define acompression chamber that decreases in volume during compression movementof the suspension assembly. The damper also includes an inertia valveincluding an inertia mass. The inertia mass is normally biased to aclosed position wherein the inertia mass is adjacent an opening to thecompression chamber such that fluid flow through the opening isinhibited and is movable to an open position wherein the inertia mass isnot adjacent the opening such that fluid flow through the opening is notinhibited. The inertia valve remains in the closed position in responseto the rider-induced pedaling forces applied to the frame and movestoward the open position in response to a terrain-induced force above apredetermined threshold applied to the wheel. The inertia valve has afirst sensitivity to terrain-induced forces in the first adjustmentposition of the sensitivity adjuster. The sensitivity adjuster isadjusted to a second adjustment position in which the inertia valve hasa second sensitivity to terrain-induced forces that is different fromthe first sensitivity. The bicycle shock absorber is operated with thesensitivity adjuster in the second adjustment position.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention can be obtained from thefollowing detailed description in conjunction with the followingdrawings, in which:

FIG. 1 illustrates a prior art rear suspension configuration for abicycle.

FIG. 2 illustrates a prior art rear suspension configuration for abicycle.

FIG. 3 illustrates one embodiment of the present invention.

FIG. 4 illustrates an embodiment of the present invention reacting to arider-induced force.

FIG. 5 illustrates an embodiment of the present invention reacting to aterrain-induced force.

FIG. 6 illustrates the fluid refill mechanism of an embodiment of thepresent invention.

FIG. 7 illustrates another embodiment of the present invention.

FIG. 8 is an enlarged schematic view of an embodiment of the presentinvention wherein the primary tube is mounted directly to an upper armmember and the remote tube is connected to an upper arm member of abicycle. An angled position of the remote tube is shown in phantom.

FIG. 9 is an enlarged schematic view of an embodiment of the presentinvention wherein the primary tube is mounted directly to an upper armmember and the remote tube and the primary tube are a single unit. Anangled position of the remote tube is shown in phantom.

FIG. 10 is an enlarged schematic view of embodiment of the presentinvention wherein the primary tube is mounted to a lever and the remotetube is connected to an upper arm member of a bicycle. An angledposition of the remote tube is shown in phantom.

FIG. 11 is an enlarged schematic view of an embodiment of the presentinvention wherein the primary tube is mounted to a lever and the remotetube and the primary tube are a single unit. An angled position of theremote tube is shown in phantom.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A damping enhancement system is described which differentiates betweenupward forces produced by the contact of the bicycle wheel with theterrain and downward forces produced by the movement of the rider'smass. In the following description, for the purposes of explanation,numerous specific details are set forth in order to provide a thoroughunderstanding of the present invention. It will be apparent, however, toone of ordinary skill in the art that the present invention may bepracticed without some of these specific details. In other instances,certain well-known structures are illustrated and described in limiteddetail to avoid obscuring the underlying principles of the presentinvention.

An Embodiment of the Damper Enhancement System

One embodiment of the present damper enhancement system is illustratedin FIG. 3. The apparatus is comprised generally of a primary tube 302and a remote tube 304 coupled via a connector hose 306.

The damper enhancement system described hereinafter may be coupled to abicycle in the same manner as contemporary shock absorbers (i.e., suchas those illustrated in FIGS. 1 and 2). For example, the damperenhancement system may be coupled to a bicycle as illustrated in FIG. 1wherein the upper mount 318 is pivotally coupled to the seat tube atpoint 106 and the lower mount 342 is fixedly coupled to the upper armmember 103. Moreover, the damper enhancement system may be coupled to abicycle as illustrated in FIG. 2 wherein the upper mount 318 ispivotally coupled to the seat tube at a point 206 and the lower mount342 is fixedly coupled to a point 204 on lever 211. These twoconstructions are illustrated in FIGS. 8-9 and FIGS. 10-11,respectively.

In addition, depending on the particular embodiment of the damperenhancement system, the connector hose may be of varying lengths andmade from varying types of material. For example, the connector hose 306may be short and comprised of metal. In this case, the primary tube 302and the remote tube 304 will be closely coupled together—possibly in asingle unit. Such a construction is illustrated in FIG. 9 and FIG. 11.By contrast, the connector hose may be long and comprised of a flexiblematerial. In this case, the remote tube 304 may be separated from theprimary tube 302 and may be independently connected to the bicycle(e.g., the remote tube may be connected to one of the wheel members suchas upper arm member 103 in FIG. 1). FIG. 8 and FIG. 10 illustrate such aconstruction, wherein the primary tube 302 is coupled to upper armmember 103 and the remote tube 304 is connected to the upper arm member103 by a connector. Regardless of how the remote tube 304 is situated inrelation to the primary tube 302, however, the underlying principles ofthe present invention will remain the same.

A piston 308 on the lower end of a piston rod 310 divides the inside ofthe primary tube 302 into and upper fluid chamber 312 and a lower fluidchamber 314 which are both filled with a viscous fluid such as oil. Thepiston rod 310 is sealed through the cap with oil seals 316 and an uppermount 318 connects the piston to the chassis or sprung weight of thebicycle (e.g., to the seat tube). A lower mount 342 connects the primarytube 302 to the rear wheel of the bicycle via one or more wheel members(e.g., upper arm members 103 in FIG. 1 or lever 205 of FIG. 2).Longitudinally extending passages 320 in the piston 308 provide forlimited fluid communication between the upper fluid chamber 312 andlower fluid chamber 314.

An inertial valve 322 which is slightly biased by a lightweight spring324 moves within a chamber 326 of the remote tube 304. The lightweightspring 324 is illustrated in a fully extended state and, as such, theinertial valve 322 is illustrated at one endmost position within itsfull range of motion. In this position, fluid flow from the primary tube302 to the remote tube 304 via the connector hose 306 is blocked orreduced. By contrast, when the lightweight spring 324 is in a fullycompressed state, the inertial valve resides beneath the interfacebetween the remote tube 304 and the connector hose 306. Accordingly, inthis position, fluid flow from the primary tube 302 to the remote tube304 through the connector hose 306 is enabled. In one embodiment, theinertial valve 322 is composed of a dense, heavy metal such as brass.

Disposed within the body of the inertial valve 322 is a fluid returnchamber 336, a first fluid return port 337 which couples the returnchamber 336 to the connector hose 306, and a second fluid return port339 which couples the return chamber 336 to remote fluid chamber 332. Afluid return element 338 located within the fluid return chamber 336 isbiased by another lightweight spring 340 (hereinafter referred to as a“fluid return spring”). In FIG. 3 the fluid return spring 340 isillustrated in its fully extended position. In this position, the fluidreturn element 338 separates (i.e., decouples) the fluid return chamber336 from the fluid return port 337. By contrast, when the fluid returnspring 340 is in its fully compressed position, the fluid return element338 no longer separates the fluid return chamber 336 from the fluidreturn port 337. Thus, in this position, fluid flow from the fluidreturn chamber 336 to the connector hose 306 is enabled. The operationof the inertial valve 322 and the fluid return mechanism will bedescribed in detail below.

The remaining portion of the remote tube 304 includes a floating piston328 which separates a gas chamber 330 and a fluid chamber 332. In oneembodiment of the present invention, the gas chamber 330 is pressurizedwith Nitrogen (e.g., at 150 p.s.i.) and the fluid chamber 332 is filledwith oil. An air valve 334 at one end of the remote tube 322 allows forthe gas chamber 330 pressure to be increased or decreased as required.

The operation of the damping enhancement system will be described firstwith respect to downward forces produced by the movement of the rider(and the mass of the bicycle frame) and then with respect to forcesproduced by the impact between the wheel and the terrain.

1. Forces Produced by the Rider

A rider-induced force is illustrated in FIG. 4, forcing the piston arm310 in the direction of the lower fluid chamber 314. In order for thepiston 308 to move into fluid chamber 314 in response to this force,fluid (e.g., oil) contained within the fluid chamber 314 must bedisplaced. This is due to the fact that fluids such as oil are notcompressible. If lightweight spring 324 is in a fully extended state asshown in FIG. 4, the inertial valve 322 will be “closed” (i.e., willblock or reduce the flow of fluid from lower fluid chamber 314 throughthe connector hose 306 into the remote fluid chamber 332). Although theentire apparatus will tend to move in a downward direction in responseto the rider-induced force, the inertial valve 322 will remain in thenested position shown in FIG. 4 (i.e., it is situated as far towards thetop of chamber 326 as possible). Accordingly, because the fluid in fluidchamber 314 has no where to flow in response to the force, the piston308 will not move down into fluid chamber 314 to any significant extent.As a result, a “stiff” damping rate will be produced in response torider-induced forces (i.e., forces originating through piston rod 310).

2. Forces Produced by the Terrain

As illustrated in FIG. 5, the damping enhancement system will respond ina different manner to forces originating from the terrain andtransmitted through the bicycle wheel (hereinafter “terrain-inducedforces”). In response to this type of force, the inertial valve 322 willmove downward into chamber 326 as illustrated and will thereby allowfluid to flow from lower chamber 314 into remote chamber 332 viaconnector hose 306. The reason for this is that the entire apparatuswill initially move in the direction of the terrain-induced force whilethe inertial valve 322 will tend to remain stationary because it iscomprised of a dense, heavy material (e.g., such as brass). Thus, theprimary tube 302 and the remote tube 304 will both move in a generallyupward direction and, relative to this motion, the inertial valve 322will move downward into chamber 326 and compress the lightweight spring324. As illustrated in FIG. 5 this is the inertial valve's “open”position because it couples lower fluid chamber 314 to remote fluidchamber 332 (via connector hose 306).

Once the interface between connector hose 306 and remote fluid chamber332 is unobstructed, fluid from lower fluid chamber 314 will flow acrossconnector hose 306 into remote fluid chamber 332 in response to thedownward force of piston 308 (i.e., the fluid can now be displaced). Asremote fluid chamber 314 accepts additional fluid as described, floatingpiston 328 will move towards gas chamber 330 (in an upward direction inFIG. 5), thereby compressing the gas in gas chamber 330. The end result,will be a “softer” damping rate in response to terrain-induced forces(i.e., forces originating from the wheels of the bicycle).

Once the inertial valve moves into an “open” position as describedabove, it will eventually need to move back into a “closed” position sothat a stiff damping rate can once again be available for rider-inducedforces. Thus, lightweight spring 324 will tend to move the inertialvalve 322 back into its closed position. In addition, the return springsurrounding primary tube 302 (not shown) will pull piston rod 310 andpiston 308 in an upward direction out of lower fluid chamber 314. Inresponse to the motion of piston 308 and to the compressed gas in gaschamber 330, fluid will tend to flow from remote fluid chamber 332 backto lower fluid chamber 314 (across connector hose 306).

To allow fluid to flow in this direction even when inertial valve 322 isin a closed position, inertial valve 322 (as described above) includesthe fluid return elements described above. Thus, as illustrated in FIG.6, in response to pressurized gas in gas chamber 330, fluid in remotefluid chamber 332 will force fluid return element 338 downward intofluid return chamber 336 (against the force of the fluid return spring340). Once fluid return element 338 has been forced down below fluidreturn port 337, fluid will flow from remote fluid chamber 332 throughfluid return port 339, fluid return chamber 336, fluid return port 337,connector hose 306, and finally back into lower fluid chamber 314. Thiswill occur until the pressure in remote fluid chamber 336 is low enoughso that fluid return element 338 can be moved back into a “closed”position (i.e., when the force of fluid return spring 340 is greaterthan the force created by the fluid pressure).

The sensitivity of inertial valve 322 may be adjusted by changing theangle with which it is positioned in relation to the terrain-inducedforce. For example, in FIG. 5, the inertial valve 322 is positioned suchthat its movement in chamber 326 is parallel (and in the oppositedirection from) to the terrain-induced force. This positioning producesthe greatest sensitivity from the inertial valve 322 because the entireterrain-induced force vector is applied to the damper enhancement systemin the exact opposite direction of the inertial valve's 322 line ofmovement.

By contrast, if the remote tube containing the inertial valve 322 werepositioned at, for example, a 45 degree angle from the position shown inFIG. 5 the inertial valve's 322 sensitivity would be decreased byapproximately one half because only one half of the terrain-inducedforce vector would be acting to move the damper enhancement system inthe opposite direction of the valve's line of motion. Thus, twice theterrain-induced force would be required to trigger the same responsefrom the inertial valve 322 in this angled configuration. FIGS. 8-11illustrate the remote tube 304 positioned at an angle from the primarytube 302 (shown in phantom). With such a construction, the sensitivityof the inertial value 322 may be adjusted as described immediatelyabove.

Thus, in one embodiment of the damper enhancement system the angle ofthe remote tube 304 in which the inertial valve 322 resides is manuallyadjustable to change the inertial valve 322 sensitivity. This embodimentmay further include a sensitivity knob or dial for adjusting the angleof the remote tube 304. The sensitivity knob may have a range ofdifferent sensitivity levels disposed thereon for indicating theparticular level of sensitivity to which the damper apparatus is set. Inone embodiment the sensitivity knob may be rotatably coupled to thebicycle frame separately from the remote tube, and may be cooperativelymated with the remote tube (e.g., with a set of gears). Numerousdifferent configurations of the sensitivity knob and the remote tube 304are possible within the scope of the underlying invention. The connectorhose 306 of this embodiment is made from a flexible material such thatthe remote tube 304 can be adjusted while the primary tube remains in astatic position.

Another embodiment of the damper enhancement system is illustrated inFIG. 7. Like the previous embodiment, this embodiment includes a primaryfluid chamber 702 and a remote fluid chamber 704. A piston 706 coupledto a piston shaft 708 moves within the primary fluid chamber 702. Theprimary fluid chamber 702 is coupled to the remote fluid chamber via aninlet port 714 (which transmits fluid from the primary fluid chamber 702to the remote fluid chamber 704) and a separate refill port 716 (whichtransmits fluid from the remote fluid chamber 704 to the primary fluidchamber 702).

An inertial valve 710 biased by a lightweight spring 712 resides in theremote fluid chamber 704. A floating piston 720 separates the remotefluid chamber from a gas chamber 718. In response to terrain-inducedforces (represented by force vector 735), the inertial valve, due to itsmass, will compress the lightweight spring 712 and allow fluid to flowfrom primary fluid chamber 702 to remote fluid chamber 704 over inletport 714. This will cause floating piston 720 to compress gas within gaschamber 718.

After inertial valve 710 has been repositioned to it's “closed” positionby lightweight spring 712, fluid in remote fluid chamber 704 will forcefluid refill element 722 open (i.e., will cause fluid refill spring 724to compress). Thus, fluid will be transmitted from remote fluid chamber704 to primary fluid chamber 702 across refill port 716 until thepressure of the fluid in remote fluid chamber is no longer enough tokeep fluid refill element 722 open. Thus, the primary difference betweenthis embodiment and the previous embodiment is that this embodimentemploys a separate refill port 716 rather than configuring a refill portwithin the inertial valve itself.

What is claimed is:
 1. A bicycle, comprising: a bicycle frame; a pedalcrank assembly supported by the bicycle frame and configured to bedriven by rider-induced pedaling forces; a wheel; and a suspensionassembly interposed between the bicycle frame and the wheel, thesuspension assembly comprising: a spring that applies a force tending toextend the suspension assembly; a damper comprising a damper tube and apiston rod supporting a piston in sliding engagement with the dampertube, the piston and the damper tube at least partially defining acompression chamber that decreases in volume during compression movementof the suspension assembly, the damper additionally comprising aninertia valve including an inertia mass, the inertia mass normallybiased to a closed position wherein the inertia mass is adjacent anopening to the compression chamber such that fluid flow through theopening is inhibited, and the inertia mass movable to an open positionwherein the inertia mass is not adjacent the opening such that fluidflow through the opening is not inhibited, wherein the inertia valveremains in the closed position in response to the rider-induced pedalingforces applied to the frame and the inertia valve moves toward the openposition in response to a terrain-induced force above a predeterminedthreshold applied to the wheel; and a sensitivity adjuster having afirst adjustment position and a second adjustment position, wherein theinertia valve has a first sensitivity in the first adjustment positionand the inertia valve has a second sensitivity in the second adjustmentposition, wherein the second sensitivity is different from the firstsensitivity.
 2. The bicycle of claim 1, wherein the piston rod occupiesan increasing volume of the damper tube during the compression movementof the suspension assembly, the damper additionally comprising a gaschamber and a barrier that separates gas in the gas chamber from dampingfluid in the damper, wherein the barrier permits a volume of the gaschamber to vary to accommodate displacement of the damping fluidresulting from movement of the piston rod into the damper tube.
 3. Thebicycle of claim 2, wherein the barrier comprises a floating piston. 4.The bicycle of claim 3, further comprising a reservoir chamber definedby the damper that accepts the displaced fluid from the compressionchamber.
 5. The bicycle of claim 4, wherein the damper further comprisesa reservoir tube that at least partially defines the reservoir chamber,wherein the floating piston is in sliding engagement with the reservoirtube.
 6. The bicycle of claim 5, wherein the gas chamber is at leastpartially defined by the reservoir tube and the reservoir tube isseparate from and non-coaxial with the damper tube.
 7. The bicycle ofclaim 5, wherein the inertia mass is positioned within the reservoirtube.
 8. The bicycle of claim 1, further comprising a valve that permitsadjustment of a pressure within the gas chamber.
 9. The bicycle of claim1, wherein the piston and the damper tube further define a reboundchamber on an opposite side of the piston from the compression chamber,wherein the piston rod passes through the rebound chamber.
 10. Thebicycle of claim 9, wherein fluid moves from the compression chamber tothe rebound chamber during the compression movement of the suspensionassembly.
 11. The bicycle of claim 10, wherein the movement of fluidfrom the compression chamber to the rebound chamber occurs through atleast one longitudinally-extending passage in the piston.
 12. A methodof providing for adjustment of a bicycle shock absorber, comprising:providing a bicycle shock absorber comprising a spring that applies aforce tending to extend the suspension assembly, a damper tube, a pistonsupported on a piston rod and in sliding engagement with the dampertube, the piston and the damper tube at least partially defining acompression chamber that decreases in volume during compression movementof the suspension assembly, the damper additionally comprising aninertia valve including an inertia mass, the inertia mass normallybiased to a closed position wherein the inertia mass is adjacent anopening to the compression chamber such that fluid flow through theopening is inhibited, and the inertia mass movable to an open positionwherein the inertia mass is not adjacent the opening such that fluidflow through the opening is not inhibited, wherein the inertia valveremains in the closed position in response to the rider-induced pedalingforces applied to the frame and the inertia valve moves toward the openposition in response to a terrain-induced force above a predeterminedthreshold applied to the wheel; providing a sensitivity adjuster for theinertia valve; providing a first adjustment position of the sensitivityadjuster in which the inertia valve has a first sensitivity toterrain-induced forces; providing a second adjustment position of thesensitivity adjuster in which the inertia valve has a second sensitivityto terrain-induced forces that is different from the first sensitivity;allowing the sensitivity adjuster to be set to either of the firstadjustment position or the second adjustment position.
 13. The method ofclaim 12, further comprising providing a knob that is operable for thesetting of the sensitivity adjuster to either of the first adjustmentposition or the second adjustment position.
 14. A method of operating abicycle shock absorber, comprising: operating a bicycle shock absorberwith a sensitivity adjuster positioned in a first adjustment position,the bicycle shock absorber comprising a spring that applies a forcetending to extend the suspension assembly, a damper tube, a pistonsupported on a piston rod and in sliding engagement with the dampertube, the piston and the damper tube at least partially defining acompression chamber that decreases in volume during compression movementof the suspension assembly, the damper additionally comprising aninertia valve including an inertia mass, the inertia mass normallybiased to a closed position wherein the inertia mass is adjacent anopening to the compression chamber such that fluid flow through theopening is inhibited, and the inertia mass movable to an open positionwherein the inertia mass is not adjacent the opening such that fluidflow through the opening is not inhibited, wherein the inertia valveremains in the closed position in response to the rider-induced pedalingforces applied to the frame and the inertia valve moves toward the openposition in response to a terrain-induced force above a predeterminedthreshold applied to the wheel, wherein the inertia valve has a firstsensitivity to terrain-induced forces in the first adjustment positionof the sensitivity adjuster; adjusting the sensitivity adjuster to asecond adjustment position in which the inertia valve has a secondsensitivity to terrain-induced forces that is different from the firstsensitivity; operating the bicycle shock absorber with the sensitivityadjuster in the second adjustment position.
 15. The method of claim 14,wherein the adjusting of the sensitivity adjuster from the firstadjustment position to the second adjustment position is accomplishedusing a knob.